1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which displays an image appearing stereoscopically by overlapping images displayed on two rear-side liquid crystal display panels which are arranged longitudinally in an overlapped manner.
2. Description of the Related Art
Patent document 1 discloses a technique which displays a three-dimensional stereoscopic image on a display screen without using special glasses or the like. In patent document 1, on a plurality of display screens having depth positions which differ from each other as viewed from a viewer, a two-dimensional image of an object to be displayed which is projected from the viewing direction of the viewer is formed. The formed two-dimensional image is displayed on a plurality of display screens having the depth positions which differ from each other as viewed from the viewer respectively, and the brightnesses of the displayed two-dimensional images are respectively independently changed for respective display screens thus forming the three-dimensional stereoscopic image.
Further, JP-A-2001-54144 (Japanese patent document 1) describes that, in this three dimensional display method, the transmissivities of two-dimensional images displayed on the respective display screens are respectively independently changed for respective display screens thus respectively independently changing the brightnesses of two-dimensional images displayed on the respective display screens.
Further, various proposals have been made with respect to the liquid crystal display device which performs the three-dimensional image display using the liquid crystal display panel. Japanese Patent 3335998 (Japanese Patent document 2) (U.S. Pat. No. 6,906,762) discloses one of such proposals in which two liquid crystal display panels overlap each other with a predetermined distance therebetween in the longitudinal direction to realize a three-dimensional image display based on the difference in parallax or the difference in motion between image data which are respectively supplied to the front-side liquid crystal display panel and the rear-side liquid crystal display panel. Patent document 2 discloses the three-dimensional image display in which the motion of the back scene data displayed on the rear-side liquid crystal display panel is small compared to the motion of front scene data displayed on the front-side liquid crystal display panel. Here, the arrangement of the front-side liquid crystal display panel and the rear-side liquid crystal display panel, the difference in motion between the back scene data and the front scene data, or both such arrangement and such difference is used as depth information for realizing the viewing of the three-dimensional image.
In this type of liquid crystal display device which overlaps two liquid crystal display panels with the predetermined distance therebetween in the longitudinal direction, a backlight is arranged on a back surface of two overlapped liquid crystal display panels and, further, display signals and drive signals for a power source and the like are supplied to two liquid crystal display panels from a drive-circuit-mounted printed circuit board which is mounted on the back surface. Here, by forming the printed circuit board using a single printed circuit board used in common by two liquid crystal display panels, the structure and the assembly of the liquid crystal display device can be simplified.    [Patent Document 1] JP-A-2001-54144    [Patent Document 2] Japanese Patent 3335998 (U.S. Pat. No. 6,906,762)
FIG. 13 is a plan view for explaining one mode of a flexible printed circuit board which is mounted on a liquid crystal display panel. FIG. 14A and FIG. 14B are side views showing a state in which the liquid crystal display panel, a backlight and a drive printed circuit board are combined with each other and the liquid crystal display panel and the drive printed circuit board are connected with each other by the flexible printed circuit board. As a method for supplying display signals and the like to the liquid crystal display panel PNL, that is, a method for driving the liquid crystal display panel PNL, a digital signal sequential transfer method (so-called data transfer method) is known as a mainstream drive method used currently. This method uses digital signals as the display signals. A plurality of data line drive circuit chips DD is mounted or formed on a long side of the liquid crystal display panel PNL, and a plurality of gate line drive circuit chips GD is mounted or formed on a short side of the liquid crystal display panel PNL.
The flexible printed circuit board FPC exhibits an L-shape in a plan view, wherein an elongated portion SF is mounted by thermo-compression bonding along the long side of the liquid crystal display panel PNL on which the data line drive circuit chips DD are mounted or formed by way of an anisotropic conductive films (ACF). A large-width portion (short-length portion) IF of the flexible printed circuit board FPC (a connecting portion for connecting the flexible printed circuit board FPC to the drive printed circuit board) has a width necessary for pulling around digital signal lines and power source lines, and is connected to the drive printed circuit board PCB. Here, the expression “large-width portion” implies that the large-width portion is a portion which is formed with a large width in general. In the liquid crystal display device shown in FIG. 14A in which the drive printed circuit board PCB is mounted on the back surface of the backlight, the large-width portion IF has a sufficient length necessary for wrapping around stacked side surfaces of the liquid crystal display panel and the backlight. Further, in the liquid crystal display device shown in FIG. 14B in which the drive printed circuit board PCB is mounted on the stacked side surfaces of the liquid crystal display panel and the backlight, the large-width portion IF is set shorter than the large-width portion IF shown in FIG. 14A.
In the liquid crystal display device which displays a stereoscopic image by overlapping two liquid crystal display panels with the predetermined distance therebetween in the longitudinal direction, it is indispensable to realize the common specification of parts for the reduction of cost and the prevention of erroneous assembling or the erroneous mounting of the flexible printed circuit board.
FIG. 15A and FIG. 15B are side views for explaining a drawback when the flexible printed circuit board having the same specification is used for a twofold liquid crystal display panel. A front-side liquid crystal display panel PNL1 and a rear-side liquid crystal display panel PNL2 are overlapped to each other with a predetermined distance D (for example, 6 mm) therebetween by interposing spacers not shown in the drawing, a backlight BL is stacked on a back surface of the rear-side liquid crystal display panel PNL2. In such structure, as a flexible printed circuit board FPC1 of the liquid crystal display panel PNL1 and a flexible printed circuit board FPC2 of the liquid crystal display panel PNL2, the flexible printed circuit board having an L-shape shown in FIG. 13 is used. Accordingly, when the drive printed circuit board PCB is mounted on the back surface of the backlight BL, it is necessary to make lengths of the large-width portions IF differ from each other as shown in FIG. 15A or it is necessary to displace positions at which the large-width portions IF of the elongated portions SF are formed from each other.
Further, when two liquid crystal display panels use a flexible printed circuit board of the same specification as the flexible printed circuit boards thereof, it is necessary to use a relay printed circuit board RPB or to slacken the flexible printed circuit board FPC1 as shown in FIG. 15B. Otherwise, it is necessary to displace the position at which the large-width portion IF of the elongated portion SF is formed.
Further, in adopting the flexible printed circuit board having the same specification, with the specification in which the flexible printed circuit board is formed in an L-shape as shown in FIG. 13, an allocating efficiency of the flexible printed circuit board, that is, a material cutting efficiency becomes low. FIG. 16 is a view for explaining material cutting of the flexible printed circuit boards shown in FIG. 13. When the L-shaped flexible printed circuit boards are allocated on a mother board sheet M-FPC, it is understood that many portions are wasted as shown in the drawing.